1. Field of the Invention
The present invention relates to a tape cassette structured such that a reel with a magnetic tape wound thereon is stored in a cassette case.
2. Description of the Related Art
Generally, a tape cassette for use in a videotape recorder and the like is structured such that a reel with a magnetic tape wound thereon is rotatably stored in the interior of a cassette case. In the central lower portion of the reel stored, there is formed an engaging portion which can be engaged with a rotary shaft provided on the reading apparatus side; and, in case where the engaging portion is engaged with the rotary shaft, the reel can be driven and rotated.
Also, on the central upper portion of the reel, there is disposed a semispherical-shaped center pin, and there is disposed a holder including a plane portion to be point contactable with the center pin in such a manner that the holder covers the center pin. The holder is always pressing the reel downwardly through an elastic mechanism and, when the rotary shaft is not connected, the reel receives the pressing force from the holder and thus the rotational movement of the reel is restricted by a stopper disposed on the cassette case side. On the other hand, in case where the reel is connected to the rotary shaft, the rotary shaft raises the reel upwardly against the pressing force to thereby remove the rotation restriction of the reel by the stopper, so that the reel is held so as to be rotatable while the upper side of the reel is supported in a point contact manner. In this state, the reel can be driven and rotated. The above-structured tape cassette is disclosed, for example, in JP-UM-B-7-18068.
By the way, the reel of the above tape cassette is structured such that it rotates while the center pin is point contacted with a pressure mechanism; and, therefore, when the reel rotates, the center pin and holder point contacted with the center pin are both shaved due to the wear thereof to thereby cause the synthetic resin, of which the holder and center pin are made, to generate the powder thereof; and, the synthetic resin powder sticks to a magnetic head to thereby give rise to the dropout of data in the recording and reproducing operations.
Also, the wear of the center pin and holder causes a core which serves as the center of rotation. That is, in case where the above tape cassette is loaded into different reading apparatus or the like and is then driven and rotated, since the rotary shaft positions of the rotary shafts are individually different according to the respective apparatus, due to the restriction of the thus-formed core, the rotary shafts are easy to incline or the centers of the rotary shafts can be easily displaced. As a result of this, the rotation torque of the reel is caused to vary, which results in the uneven rotation of the reel and also in the vibrations of the reel.
In view of the above problems, according to JP-UM-B-7-18068, the center pin and a member to be point contacted with the center pin are both made of resin material having high wear resistance. However, especially in order to meet the need for enhancement of the rotation speed of the reel involved with realization of the increased capacity of the recording capacity in recent years, when the reel is rotated at a high speed, even in case where the center pin and its mating member are made of the above resin material, they wear, thereby raising a similar problem to the above problem. That is, in order to enhance the handling efficiency of the magnetic tape for quick recording and writing data into the magnetic tape, in case where the normal high-speed rotation of the magnetic tape, namely, about 2000 rpm is increased up to about 3000˜4000 rpm, wear is easy to occur and, even in the case of slight wear, the rotation torque of the reel is caused to increase, thereby raising a fear that the dropout of data can occur.